The present disclosure relates to a development device that can be installed suitably in an image forming apparatus such as a copier or a printer, and an image forming apparatus including the development device.
A conventional development device includes a development housing having a development roller and a stirring screw, and a toner container that replenishes toner and is attached to the development housing detachably. A toner discharge port that can be opened and closed is provided in a bottom portion of the toner container, and a toner replenishment port is provided in the development housing in a position corresponding to the toner discharge port. When the toner container is attached to the development housing and both the toner discharge port and the toner replenishment port are opened, toner in the toner container is supplied to a predetermined circulatory conveyance passage formed in the development housing.
The circulatory conveyance passage is constituted by an outward conveyance passage corresponding to the toner replenishment port and a return conveyance passage corresponding to the development roller. A stirring screw in which a spiral vane is disposed around a rotary shaft is mounted in each circulatory conveyance passage. The toner is conveyed in circulatory fashion between the outward conveyance passage and the return conveyance passage by the respective stirring screws.
In a conventional development device having this type of configuration, a conveyance ability suppressing portion may be provided on the stirring screw provided in the outward conveyance passage on a downstream side of the toner replenishment port in order to reduce a conveyance ability locally. A toner accumulation portion is formed by the conveyance ability suppressing portion in the vicinity of the toner replenishment port on an upstream side of the conveyance ability suppressing portion. When a large amount of toner exists in the accumulation portion, the toner in the accumulation portion blocks the toner replenishment port. Further, when the amount of toner in the accumulation portion is small, a gap is formed between the toner replenishment port and the toner accumulation portion such that toner flows into the development housing from the toner container side. Thus, an amount of replenishment toner supplied to the development housing from the toner container is regulated in accordance with the amount of accumulated toner in the accumulation portion.
When determining an interior layout of an image forming apparatus main body installed with the development device described above, it may be desirable to connect the toner container to an end portion of the development housing in an extension direction of the rotary shaft. In this case, the toner replenishment port is disposed in an end portion of the outward conveyance passage. However, a connecting passage connecting the outward conveyance passage to the return conveyance passage is close to this end portion, and therefore developer accumulates easily therein. Hence, when the toner replenishment port is disposed in the end portion of the outward conveyance passage, developer accumulation in the vicinity of the connecting passage affects the accumulation portion formed by the conveyance ability suppressing portion, and as a result, toner replenishment regulation becomes unstable.
An object of the present disclosure is to provide a development device in which replenishment developer is supplied from a replenishment developer housing portion as an amount of developer in a developer accumulation portion decreases, with which the replenishment developer can be supplied with stability even when a developer introduction port is disposed in the vicinity of a connecting passage of a developer conveyance passage.